My Wrekin

Ductile Iron FAQs

What is ductile iron?

Ductile iron is a unique form of graphite-rich cast iron which has been treated before the casting process to produce an exceptionally strong and durable material with high impact resistance.

It is also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron. It has a much superior strength to weight ratio than traditional grey cast iron.

This combination of properties allows us to design and produce our innovative features and make significant weight savings that could not be achieved with less sophisticated materials.

What type of sealing arrangement is the cover supplied with?

A15 to C250 ductile iron manhole covers have a single integral, ‘dry-labyrinth’ (tongue and groove) seal, whereas D400 to F900 have no integral seals unless otherwise stated in their datasheets. Some steel manhole covers have a single integral seal, where others have no seal (at the same load category). The datasheets provide details of the existence of seals.

What pressures are the manhole cover seals rated to?

Standard manhole cover seals are designed to resist water/odour egress/ingress at normal atmospheric pressure only. For higher pressure requirements (up to 0.5Bar), a flood & odour control plate should be used.

What is the coating that the covers are painted with?

The bituminous coating found on our covers is a barrier coat intended to provide some aesthetic appeal and a low level of corrosion protection. Under normal UK non-marine exposure conditions, it is not necessary to provide additional protection to ductile iron castings, as any initial surface oxidation (rust) prevents further corrosion. Rust is not thought to reduce the life of ductile irons.

Why are ductile iron manhole covers and gratings only available in fixed sizes?

To produce a casting, a pattern must be used which is an expensive piece of equipment. For this reason, generally, only standard chamber sizes are accommodated by castings unless quantities allow economic manufacture of covers to non-standard chamber sizes. Custom-sized covers are often accommodated by the manufacture of a bespoke steel fabrication.

Can Wrekin’s access covers and gratings be locked?

Most of Wrekin’s products offer screw-fastener locking as a factory-fitted option, whilst some products incorporate dedicated lock assemblies as standard. Where locking is available or as a standard fitment, this is illustrated on the respective product datasheet. In some circumstances, it may also be possible to factory lock other products on request.

What are the CD526 water evacuation rates for Wrekin’s gully gratings?

The water evacuation rates for Wrekin gully gratings vary depending on the design of the gully. Generally, for conventional designs, the larger the grating the greater the capacity for water evacuation. CD526 categories are available for all Wrekin gratings within the product data.

What are the link fasteners for between double triangular covers?

The purpose of link fasteners between adjoining cover elements is to provide a loose coupling that reduces the possibility of dropping a joined-pair of covers down a chamber during cover lifting. At the same time, they must allow the covers to perform independently under traffic loads so must remain loosely fastened in all circumstances.

Note: Link fasteners are not actually applied to help traffic security but will make some contribution to it in the event of unrestrained cover movement.

Are all gully grating tops reversible for opposite hinging applications? e.g. one-way streets, traffic islands, etc.

Not all of them are reversible. Usually they are reversible where provisions are made in the frame to allow it. This is usually restricted to loose-fit, flat seated designs like Highway double-triangular gully gratings. Reversibility is not possible where there are no provisions in the design. It is usually restricted to interference-fit, wedge seated designs which are manufactured to a specific orientation and component pairing.

What type of Wrekin product data can be provided for enquiries?

Wrekin can provide datasheets and safety information which provide the fundamental dimensions and product details. On request, additional illustrative drawings and documents may be provided at Wrekin’s discretion, including further data for BiM purposes.

Clear opening vs base opening vs clear area?

How access covers are measured:

Manhole Cover Gully Grate Clear Opening Measurements

Access cover dimensions are always referred to by their ‘clear opening size’ and sometimes also by their frame depth (see diagram).

Clear Opening:

The clear opening is the inside frame dimensions and these should normally be marked on the cover. If these are missing or have become illegible over time then it will be necessary to remove the cover and physically measure these dimensions. The clear opening size of the access cover frame must always be equal to or greater than the size of the chamber it is covering to ensure the frame is adequately supported.

Base Opening:

These are the most important dimensions when establishing the correct size of frame intended to fit on a given chamber or gully-top opening. i.e. The central opening at the base of a frame must never be smaller than the opening at the chamber top so that the frame flange is always completely supported by the chamber top, usually via bedding materials. This harmonisation of component dimensions is vital in achieving the most effective traffic-load transfer possible to an underlying chamber structure.

Clear Area:

The Clear Area dimensions are the two gross measurements taken perpendicular to each other and a product’s permanent frame walls or supports and which coincide with the narrowest points at that location. In view of this, it is common for one of these dimensions to be the same as the Clear Opening.

A frame product’s Clear Area often disregards the presence of cover seating or locking-feature encroachment in the corners of the frame. i.e. Such features are generally ignored as their presence is generally not considered detrimental to unrestricted chamber access unless the equipment in a given chamber requires the full use of a frame product’s Clear Area.

How do I know if I need 100mm or 150mm frame depth?

Minimum frame depths for NRSWA road category Types 0 to 4 shall be as Table A (below). Manhole covers in shared driveways that could be subject to occasional loads from heavy vehicles (e.g. refuse vehicles) should see the requirements for Type 4 roads. Although the frame depths are prescribed in the NRSWA, the location of the (immovable) chamber top relative to the finished road surface, may sometimes dictate the depth of frame that can be accommodated.

Road type Taffic capacity Road application Minimum frame depth (mm)
Type 0 30-125 msa Trunk roads and dual carriageways 150
Type 1 10-30 msa All other A roads 150
Type 2 2.5-10 msa Bus services 150
Type 3 0.5-2.5 msa All other roads except residential cul-de-sacs 150
Type 4 Up to 0.5 msa Residential cul-de-sacs 100

Table A

Care and Adaptation

My customer has installed a manhole cover and frame (MHC), is it possible to retro fit a flood & odour-control plate?

At present, it is not possible to retro-fit a flood & odour-control plate to our Highway and TriStar ranges. Unite manhole covers do have the facility for retro-fitting new low-leak and no-leak seal plates.

If you do require a flood and odour control plate you can exchange stock before installation or re-install the MHC, replacing it with one incorporating a factory fitted flood & odour control plate. 

Can I recoat my cover as the coating has eroded from traffic and it’s starting to rust?

Yes. Manhole covers and gratings can be recoated with any paint suitable for ferrous metal which does not unduly compromise a product’s skid resistance. However, due to bitumen residues from the original coating process, we recommend using a bitumen compatible paint e.g. ‘Johnstone’s Black Bituminous Coating’.

My manhole cover looks rusty. Is this a problem?

Bitumen coating acts as a barrier coat for transportation and short-term aesthetic purposes only and provides no electrolytic corrosion protection to the underlying iron. Where light rusting or corrosion has occurred on the upper surface of an iron access cover or grating product, this will have no effect on the function of the product and will certainly not affect its structural integrity.

Classification and Standards:

Wrekin is the first company to have all its ductile manhole covers and gully grates Kitemarked by the British Standards Institute to the new BS EN 1242:2015.

Should manhole covers have their load classification marked on them?

Yes. It is a requirement of the BS EN124-2:2015 that all manhole covers and gratings claiming conformance to this Standard clearly identify their load class on the top face of the cover or grating to provide guidance on where they can be installed to suit the anticipated traffic exposure.

If a cover is badged D400 can it be used in all categories of road?

In essence, yes, where the vehicle types employ pneumatic tyres. The difference between the ranges at the same D400 load classification is mostly related to durability and expected service life, but all should be capable of installation in a BS EN124 Group 4 (highway) location. E600 load class products are sometimes specified for certain highway applications but this is often due to inadequate D400-design products not fulfilling the Group 4 location traffic function. Indeed, installations incorporating inadequate E600-design products can be just as vulnerable to premature failure.

Is CE marking a requirement for Wrekin access covers?

CE marking is only a requirement for products covered by a harmonised European standard covered by the Construction Product Regulations. At present (November 2016), the controlling standard BS EN124 for access covers and gratings of up to 1m clear opening, is not harmonised, hence, there is not a current requirement to CE mark products supplied against this standard.

Where a product carries a Kitemark, what does this actually mean?

Where a product carries a Kitemark or other Third Party Certification (TPC) mark, it indicates that the product has been tested by an accredited independent body and has achieved all the requirements of the relevant standard. On our products, Kitemark is the TPC mark for BSi (British Standards Institute).

With the introduction of BS EN124-2015, are there any associated changes in installation practice for Wrekin’s products?

Not at the moment. Exceptions may come with the introduction of new products. Any variations from the recommended standard installation practice of using UniPak Mortar and adjustment unit accessories will be advised of on our website and/or literature.

What constitutes a seal in relation to BS EN124-2015 manhole and access covers?

Seals are features of manhole covers or access cover assemblies which provide resistance to fluid and gaseous egress or ingress. Unless otherwise described, seals are only designed to provide resistance to leakage at normal atmospheric pressure. Should an application require resistance to higher operating pressures, please clearly state this so a suitable product can be selected. Typical seal arrangements are illustrated on the final page of this document.

Day-to-day Operation

How many 25Kg tubs of UniPak mortar do I need to install my manhole cover?

There is no definitive quantity of mortar, the amount needed depends on the volume or size of gap below the frame that needs filling and whether other adjustment unites are to be used in the bedding construction.

The general rule for calculation is based on a cured mortar density of 2,000Kg/m³. Wrekin can provide guidance on this for a given product size and known bedding depth.

Do Wrekin’s access covers or gully gratings require periodic maintenance?

Currently, none of the cast assemblies require periodic maintenance, although it is good practice to clean all seatings and cover/frame clearances when chamber access has been completed. Cover/ lid lifting keyways not already containing Wrekin’s anti-blockage keyway component may require cleaning out before cover removal to allow lifting key fitment.

What does Wrekin supply or recommend for access cover lifting purposes?

Over time, access covers can accumulate debris in crevices and clearances which can affect their static lifting weight. In view of this, and the fact that cast iron products are usually of significant mass, we recommend that mechanical lifting devices are used wherever possible to lift access covers from their frames. Where manual lifting is required or preferred, Wrekin offers a range of lifting keys suitable for all common access cover types.

My manhole cover is stuck in its frame and I’m struggling to open it with lifting keys. What should I do?

If there are prising slots available at the cover perimeter, use a suitable prising bar (e.g. crow bar) to ease it open, then use the lifting keys to complete the cover removal. If there are no prising slots, clear the gaps between the cover and its frame and then strike the cover in the geometric centre with a mallet or lump hammer (<5Kg) so that the material’s elasticity is used to ‘bounce’ the cover and break its stickiness in the frame.

Note: This ‘bounce’ technique should not be used on Class A15 covers or those in-filled with brittle surface materials.

Is there any way I can stop the lifting keyways in my manhole covers from becoming blocked?

Yes, if buying new from Wrekin, ask if the product being offered has the option of the Anti-Blockage Insert. Alternatively, if it’s existing products that require the anti-blockage feature, determine the approximate internal dimensions of the keyways as it may be possible to fit our standard items due to their universal-fit characteristics.

Can I interchange manhole cover lids between frames of identical product types?

We do not recommend this as cast components are usually paired at the manufacturing foundry, so that the likelihood of combining components not originally assembled together at the foundry, may not result in stable cover operation. If this process is unavoidable or preferred, please consult Wrekin Technical office for advice.

What does Wrekin’s enhanced anti-skid coating provide in terms of traffic skid resistance?

The factory application of Wrekin’s enhanced antiskid coating enhances the surface skid resistance of conventional cast iron manhole covers to a PSRV value in excess of that required by CD 534 (formerly Highways England HA104/09) requirement for high skid-risk areas. Our enhanced anti-skid coating is manufactured from materials typically used in road anti-skid surface treatment applications. This means it benefits from the significant advantage of having its wear characteristics closely follow those of the surrounding road surface, which is a fundamental requirement in reducing the likelihood of induced vehicle-skid (from surfaces having differential skid resistance).